1. Field of the Invention
The present invention relates to a vehicle control device for engine control, transmission control, or the like for arithmetically processing a control amount according to a control program by using a microcomputer and, more particularly, to a vehicle control device in which a memory for storing a control program can be updated while being incorporated in the control device.
2. Description of the Related Art
Since a vehicle control device is generally under severe conditions such as temperature or vibration, a socket, for attaching a ROM (Read-Only Memory) or the like for storing a control program for engine control, cannot be used. For this reason, a program is written in the memory by a single-purpose machine before the control device is assembled, and the memory is directly soldered on a substrate.
For example, in a vehicle control device which controls an engine (i.e., an engine control device), the contents in a ROM may need to be changed due to a mismatch between control data of respective engines in mass production or the like.
In this case, in a conventional technique, the ROM is once removed and updated, and then must be resoldered. As a result, there are problems such as an increase in number of production steps, and the degradation of the reliability of the soldered portion.
To solve the above problems, in a conventional engine control device described in Japanese Patent Publication No. 8-2556562, in a change of the contents of a ROM, a new program is written in the ROM while the ROM is attached to a substrate.
However, such a conventional device has no countermeasure against a writing defect occurring when a signal is stopped due to some factor such as the instantaneous cut-off of the operation of a line (communication signal line) in the middle of an updating operation. In a checking step following the writing operation, the ROM on which data is written must somehow be checked. For this reason, the number of operation steps increase in number, and productivity is degraded. In addition, the result of such a checking step can be overlooked.
In this case in which the result of the checking step is overlooked, it may happen the above writing defect is manifested as a control amount which is apparently abnormal under almost all operating conditions. If this happens, the overlooking of the check result in the checking step could still be detected in some step that follows the checking step. However, when the writing defect is such that there is a control amount which is abnormal under only a special condition, the overlooking of the check result cannot thereby be detected, and the defective products disadvantageously can issue to the market.